The present invention relates generally to stabilized particles and methods for their production. More specifically, the present invention relates to particles having a size of less than about 0.1 microns or 100 nm, such as nanoparticles, that are stabilized by an insulating, semiconducting and/or metallic coating.
Nanosized metal particles have a wide variety of potential uses, ranging from nonlinear optical switching and high-density information storage to immunolabeling and tracer diffusion studies in concentrated dispersions. Nanoparticles have unique optical, electrical and magnetic properties. Nanoparticles are typically optically transparent. A major difficulty with large-scale implementation is that metal colloids have complicated double-layer structures, and their stability is controlled by both electronic equilibria and ionic/polymer adsorption.
Semiconductor materials also have an extraordinary importance in technology mainly because of their special electronic properties that arise from a separation between the conduction and valence bands. When semiconductor materials are prepared in the nanoparticle-size range, the density of electronic states changes in a systematic manner which strongly influences the optical and electronic properties of the material. The surface of semiconductor nanoparticles is highly defective from the point of view of semiconductor physics, so that energy levels within the energy gap of the bulk solid occur due to reconstruction of atomic positions.
The preparation of at least nanosized particles can be facilitated greatly by careful choice of the ligands or stabilizers used to prevent particle coalescence. For example, polymeric stabilizers are very efficacious dispersants in aqueous solution, whereas long chain surfactants or chemically specific ligands are more widely used in organic media. Alternatively, stabilization can be achieved through compartmentalization of the particles in micelles or microemulsions, while immobilisation in glasses or sol gels is the preferred technique when redox reactions of the particles with the matrix need to be avoided. More recently, Langmuir-Blodgett (LB) films have been used as particle stabilizers, and electrodeposition of surfactant-stabilized metal particles has been used to create ordered two-dimensional crystals. These various techniques not only permit the synthesis of pure metal particles, but also allow the preparation of semiconductor particles and nanosized alloys, mixed metal particles, and coated particles as well as particles with nonspherical geometries (e.g., rods or platelets).
However, many of the stabilizers employed affect the solid state properties of the particles. To circumvent this problem it is desirable to find a stabilizer that prevents particle coalescence. In addition, it is preferable that the stabilizer be chemically inert and optically transparent. These conditions can be met by, for example, silica, a coating material used in a wide range of industrial colloid products ranging from paints and magnetic fluids to high quality paper coatings.
The use of silica as a stabilizer rather than an organic molecule has several advantages. In addition to preventing coagulation of the particles during chemical or electronic processes, the silica shells are expected to act as a passivant due to a disordered (amorphous) structure that can be accommodated to that of the underlying particles.
However, some particles, for example, gold metal, have very little affinity for silica because they do not form a passivating oxide film in solution. furthermore, there are usually adsorbed carboxylic acids or other organic anions present on the surface of such metals to stabilize the particles against coagulation. These stabilizers also render the metal surface vitreophobic.
A need exists for a method of coating particles with a suitable agent such as silica to impart stability to the particles and to the surface thereof without substantially affecting their properties, in particular their optical properties such as fluorescence.
Accordingly, it is an object of the invention to address the above-identified need in the art.
According to one aspect of the present invention there is provided a method of stabilizing particles with an insulating, semiconducting and/or metallic coating. The method comprises: (i) admixing a source of particles with a source of coating to provide a particle-coating admixture; (ii) adding to the particle-coating admixture a bifunctional ligand represented by structural formula (I)
Axe2x80x94Xxe2x80x94B,xe2x80x83xe2x80x83(I)
wherein A is a first functional group that attaches to the particle, or to a coating formed on the particle, selected from the group consisting of thiols, amines, phosphines, phosphates, borates, tetra alkyl ammoniums, carboxyls, silicates, siloxys, selenates, arsenates and aluminates, B is a functional group that activates the surface of the core particle for nucleation of a coating layer and is selected from the group consisting of thiols, amines, phosphines, carboxyls, silicates, siloxys, silanes, selenates, arsenates and aluminates, and X is an optional linking group.
In an alternate embodiment, the source of particles is first admixed with the bifunctional ligand to provide a particle-ligand admixture; (ii) adding to particle-ligand admixture a source of coating; and (iii) allowing the bifunctional ligand and coating to deposit on the particles.
According to another aspect of the invention, stabilized particles are provided wherein the particles are prepared by either of the aforementioned methods.
According to yet another aspect of the present invention, there are provided particles stabilized by an insulating, semiconducting and/or metallic coating, wherein said coating is attached to said particles via a bifunctional ligand.
According to still another aspect of the present invention, a method is provided for determining the presence of an analyte in a sample suspected of containing the analyte comprising incubating the sample with a ligand that specifically binds to the analyte and is capable of providing a detectable signal, wherein the ligand comprises a coated particle as disclosed herein.
According to a further aspect of the present invention there is provided a pigment or paint colourant which is composed wholly or partly of the stabilized particle defined above.
These and other embodiments of the subject invention will readily occur to those of ordinary skill in the art in view of the disclosure herein.